How to avoid noisy renders in Cycles?
Samples:
What you want is the number of Samples.
A Sample refers to cycles firing a &quot;ray&quot; into the scene and returning information based on the color and other properties of objects it interacts with.
E.g. If a ray bounces off a red object and then hits a light source, the corresponding pixel will get a red color.
Also see Why can&#39;t cycles cast one ray per image pixel, instead of rendering progressively to infinity?
You can change the number of samples taken per pixel in Render settings &gt; Sampling &gt; Samples &gt; Render:

Increase this value to take more samples and reduce noise. See the manual:

There are two integrator modes that can be used: path tracing and branched path tracing. The path tracing integrator is a pure path tracer; at each hit it will bounce light in one direction and pick one light to receive lighting from. This makes each individual sample faster to compute, but will typically require more samples to clean up the noise.

Progressive refine:
Progressive refine does not change the number of samples, it disables tiled rendering. With tiled rendering each tile is rendered to the full number of samples before starting the next. Disabling this is useful for rendering the entire image all at once, so the user can manually stop the render and get a finished image.
Note that the render will still stop at the number of samples defined in Sampling &gt; Samples &gt; Render using this setting, and rendering the entire image this way is much slower than rendering with tiles.